Various methods have been employed to electronically control water flow through a faucet or spout. Predominant among the accepted methods is the use of an optical sensor, preferably comprised of a pulsed infrared ("IR") emitter and an IR detector which, together with processing electronics, are used to control one or more solenoid valves. In this method, the reflections of a pulsed IR beam from objects (e.g., a user's hands) are sensed and used to determine whether to activate or deactivate a solenoid valve. Pulsed IR sensing has been dominant due to its reasonable performance and low cost. Pulsed IR processing circuitry typically consists of some mixed analog and digital components and perhaps even a microprocessor.
Prior art pulsed IR sensors of the type made integral to a faucet have substantial problems arising from a need to suppress reflections from the water stream itself. As is well known in the art, the water stream reflects near-IR light. The resulting reflections of IR signals from the water stream when an IR emitter is mounted behind an aerator has caused engineers to design optical paths that avoid such reflections. If the reflection is not avoided, the water stream can create enough of a reflection to force the solenoid valves to "lock-on", causing a waste of water and a great annoyance to the user. Under such conditions, only when the electronics "times out" and deactivates the electric valve will water flow ultimately cease. The total elapsed time period of a lock-on can be as long as several minutes, depending on the preset time-out delay chosen by the manufacturer.
One approach to avoiding water stream reflections is disclosed in U.S. Pat. No. 5,025,516, wherein the optical paths of the IR emitter and IR detector are made convergent to a zone just behind the water stream and just short of the basin. Other known approaches involve: 1) emitting a narrow beam of IR to one side of the water stream; 2) emitting the IR at a sufficiently oblique angle to the water stream that no reflections from it are detected; or, 3) decreasing the sensor's overall sensitivity. Sensors using the latter approach have difficulty adequately sensing hands with dark skin color, and also provide poor detection continuity.
The chief problems with convergent optics are: 1) A narrow detection field, with a resulting poor tolerance to variations in the hand positions needed either to initiate water flow or to maintain water flow continuity; 2) an increase in product cost as a result of the need for lenses or other focusing means, and; (3) a need for greater complexity in the mechanical configuration of the water spout itself to accommodate the optics needed to generate the convergent optical beams.
Another common problem with existing sensor designs is the inability to recover from common and unavoidable environmental problems, such as water and/or soap films running down the optical lenses, paper towels thrown over the spout, debris left in the basin, etc. Such occurrences cause reflective IR signal changes that existing sensor designs are poorly equipped to tolerate. For example, a soap bubble clinging to an optical lens can bias the optical background reflection higher and thereby make the sensor more sensitive to a subsequent detection. If a great enough optical feedback path is created, the sensor can begin to run continuously until the sensor times out and shuts down. Likewise, a paper towel draped over the spout can cause the water to run on for a long time, also creating a time-out condition resulting in complete inoperability. In fact, the only reasonable recourse for existing sensor designs has been to shut down and become completely inoperable in the face of a soap bubble or foreign object that causes enough signal reflectance to create a permanent trigger. U.S. Pat. No. 4,682,628 describes such a method. Only when the obstruction is removed will such a sensor recover and begin to operate once again.
Another shortcoming of existing sensor designs is an inability to adapt to changes in background signal level associated with a gradual discoloration of the sink, a gradual degradation of the lens due to the use of abrasive cleaning compounds, a gradual degradation of the IR emitter performance, and the like. Existing sensors employ a fixed sensitivity threshold which is set either at the factory or by the installer (or both). Subsequently, as sensitivity is affected by environmental factors, the sensor's performance will degrade, and may fall off far enough to warrant a service call. More likely the gradual degradation will not be noticed, and the poor performance will be taken by the users as "normal".
It is generally recognized that automatic faucets are often installed by individuals who have limited electronics skills and who are not cognizant of proper methods for setup and adjustment. Existing sensor designs usually require the installer to make some adjustment in sensor sensitivity. Even if such an adjustment is not required (e.g., when preset at the factory) the mere presence of an adjustment invites the installer to "play" with the sensitivity control, often in a deleterious manner.